JP5186694B2 - Method for producing chitin nanofiber, composite material and coating composition containing chitin nanofiber, and method for producing chitosan nanofiber, composite material and coating composition containing chitosan nanofiber - Google Patents

Description

  The present invention relates to a method for producing chitin nanofibers from a chitin-containing bio-derived material, chitin nanofibers obtainable by the method, and a composite material and a coating composition containing the chitin nanofibers. The present invention further relates to a method for obtaining chitosan nanofibers from a chitin-containing bio-derived material, and a composite material and a coating composition containing the chitosan nanofibers.

  Nanofibers are ultrafine fibers that generally have a diameter (width) of several tens to several hundreds of nanometers, and have features such as a significantly larger surface area than conventional fibers, and thus exhibit new and special functions. It is attracting attention and is being used. Polymer materials such as nylon and polyester are mainly used as raw materials for nanofibers. Recently, active research has been conducted on obtaining nanofibers from biological materials and using them for environmental considerations. Has been made.

  Chitin and chitosan are also derived from living organisms, and research into nanofibers is being conducted. For example, there is a method in which commercially available chitin is defibrated and dried into nanofibers using a rotary desk wet pulverizer (Patent Document 1, Patent Document 2), but commercially available chitin forms hydrogen bonds extremely strongly between fibers. Even when a physical load is applied, it is difficult to completely loosen the fiber, and therefore the shape of the fiber is uneven. There are also examples in which chitosan is dissolved in a solvent and nanofibers are spun by electrospinning (Patent Document 3, Non-Patent Document 1), but it is necessary to dissolve chitosan once in a solvent, Heavy load and unsuitable for mass production. The fiber obtained by electrospinning has a large diameter (fiber width of 100 nm or more) and is not uniform. In addition, mass production is difficult with the electrospinning method, and the energy cost is high. Moreover, since chitin is insoluble in a solvent, chitin nanofibers cannot be produced by electrospinning. Although there is also a method of obtaining bionanofiber by hydrolysis (Non-patent Document 2), the fiber is cut by acid treatment, so the fiber length is shortened to 1 μm or less. There is a method in which commercially available chitin is oxidized using a TEMPO catalyst to increase the dispersibility in water and the nanofibers are defibrated by ultrasonic treatment (Non-patent Document 3). It is decomposed and the fiber length is greatly reduced. The result is more like a whisker than a fiber. Strictly speaking, the chemical structure is different from that of chitin because of the oxidation treatment. There is also a method in which acetic acid is added to chitin derived from squid tendon to form nanofibers by ultrasonic treatment (Patent Document 4, Non-Patent Document 4). Squid-derived chitin is a beta chitin with a low degree of crystallinity, so it can be easily loosened and can be made into nanofibers, but crab / shrimp shell-derived chitin is a highly crystalline alpha chitin with high mechanical strength. Chitin nanofibers cannot be obtained even after treatment. Furthermore, since the squid tendon is overwhelmingly scarce in resources compared to crab and shrimp shells, the possibility of practical application of the above method is low.

  Crustaceans such as crabs and shrimps contain abundant chitin in their outer shells. Moreover, shrimp and crabs are consumed in large quantities. In most cases, these hulls are discarded. In order to make effective use of these resources, some attempts have been made to produce nanofibers by obtaining chitin from crustaceans. However, no chitin nanofibers have been obtained from these organisms as they are, thin, long, homogeneous, and excellent in crystallinity, physical properties, ease of processing operation, and accumulated amount.

Research has also been conducted on the use of biological nanofibers, and they have been put into practical use. For example, paints using chitosan have been commercialized, but since chitosan is soluble only in acidic solutions, paints using chitosan are not suitable for metals. In addition, since chitosan is highly hygroscopic, paints using chitosan need to be applied in places with air conditioning equipment in summer.
JP 2003-155349 A Japanese Patent Laid-Open No. 4-281017 JP 2007-236551 A JP 2009-102782 A Min B. et al., Polymer, 2004, 45, 7137 Gopalan N., et al., Biomacromolecules, 2003, 4, 657 Fan Y. et al, Biomacromolecules, 2008, 9, 192. Fan Y. et al, Biomacromolecules, 2008, 9, 1919.

  It was an object of the present invention to obtain chitin nanofibers that are thin, long, homogeneous, and excellent in crystallinity, physical properties, ease of processing operation, and accumulated amount from materials derived from chitin-containing organisms. And it was the subject of this invention to develop the use of chitin nanofiber. Similarly, obtaining a chitosan nanofiber having excellent properties and developing its application was also an object of the present invention. For example, it has been one of the specific problems of the present invention to develop a paint that eliminates the drawbacks of conventional chitosan paints.

  As a result of intensive studies in view of the above problems, the present inventors have obtained a thin, long, homogeneous, crystalline property, physical property, and ease of processing operation from a chitin-containing organism-derived material, with almost no damage. We have developed a manufacturing method to obtain chitin nanofibers that are excellent in any amount of accumulation. By including chitin nanofibers in the composite material, the present inventors have succeeded in producing a composite material that has less thermal expansion than the conventional one and that does not lose light transmission and flexibility. Furthermore, by including chitin nanofibers in the coating composition, a coating film more uniform than the conventional one was formed, and a coating composition having excellent adhesiveness was successfully produced. In addition, chitosan nanofibers having excellent properties, and composite materials and coating compositions containing chitosan nanofibers have also been successfully produced from biotin-derived materials.

  The chitin nanofiber derived from a chitin-containing organism-derived material obtained by the present invention is thin, long, homogeneous, and excellent in any of crystallinity, physical properties, ease of processing operation, and accumulated amount. Therefore, it can be applied to many uses. The composite material containing chitin nanofibers, particularly the chitin nanofibers obtained by the present invention, has less thermal expansion than the conventional ones, and the light transmittance and flexibility are not lost. The coating composition containing chitin nanofibers, especially chitin nanofibers obtained by the present invention forms a more uniform coating film than the conventional one and has excellent adhesiveness. Furthermore, since the coating composition of the present invention can be made into a neutral coating composition, it can be applied to metals, has a low hygroscopic property, and does not require air conditioning during painting. Chitosan nanofibers obtained by the present invention, composite materials containing the same, and coating compositions also have excellent properties.

FIG. 1 is a photograph taken by a scanning electron microscope (FE-SEM) of a chitin nanofiber derived from a crab shell obtained by the method of the present invention. The magnification on the left is 20,000 times, and the magnification on the right is 70,000 times. FIG. 2 is a spectrum of chitin nanofibers derived from crab shell obtained by the method of the present invention, using an infrared spectrophotometer (FT-IR). FIG. 3 is an X-ray diffraction pattern obtained by an X-ray scattering measurement apparatus for chitin nanofibers derived from crab shells obtained by the method of the present invention. FIG. 4 is a photograph taken with a scanning electron microscope (FE-SEM) of chitin nanofibers derived from shrimp shells obtained by the method of the present invention. The magnification is 30,000 times. FIG. 5 is a diagram showing the results of measuring the transmittance of the crab shell-derived chitin nanofiber-containing composite material obtained by the method of the present invention using an ultraviolet-visible spectrophotometer. In the photograph on the right side of the graph, the top shows the flexibility of the chitin nanofiber-containing composite material of the present invention, and the bottom is the chitin nanofiber sheet (no resin). FIG. 6 is a diagram showing a result of measuring thermal expansion by a thermomechanical measuring device of a crab shell-derived chitin nanofiber-containing composite material obtained by the method of the present invention. In the photograph on the right side of the graph, the top shows the flexibility of the chitin nanofiber-containing composite material of the present invention, and the bottom is the chitin nanofiber sheet (no resin). FIG. 7 is a photograph taken by a scanning electron microscope (FE-SEM) of chitosan nanofibers derived from shrimp shells obtained by the method of the present invention. The magnification is 100,000 times.

Accordingly, the present invention provides the following.
(1) Chitin-containing biological material
Subject to at least one deproteinization step and at least one decalcification step;
A method for producing chitin nanofibers, which is subjected to a defibrating process.
(2) The method according to (1), further comprising a step of treating with an acidic reagent before the defibrating step.
(3) The method according to (2), wherein the acidic reagent is a weak acid and the pH in the treatment step is 3 to 4.
(4) The method according to any one of (1) to (3), wherein each step is always performed without drying (5) The chitin-containing organism is a crustacean, according to any one of (1) to (4) Method.
(6) A chitin nanofiber obtained by the method according to any one of (1) to (5).
(7) The chitin nanofiber according to (6), wherein the fiber has a width of 2 nm to 20 nm.
(8) The chitin nanofiber according to (6) or (7), wherein the fiber state is an extended chain crystal.
(9) A composite material containing chitin nanofibers and a resin.
(10) The composite material according to (9), wherein the coefficient of thermal expansion is reduced to 2 × 10 ⁻⁵ ° C. ⁻¹ or less.
(11) The composite material according to (9) or (10), wherein the transmittance loss at 600 nm is 10% or less as compared with a material containing no chitin nanofibers having the same thickness.
(12) The composite material according to any one of (9) to (11), wherein the chitin nanofibers are those according to any one of (6) to (8).
(13) A method for producing a composite material, wherein a resin monomer is polymerized in the presence of chitin nanofibers.
(14) The method according to (13), wherein the chitin nanofiber is any one of (6) to (8).
(15) A coating composition comprising chitin nanofibers and a water-soluble resin or emulsion.
(16) The coating composition according to (15), which is for metal.
(17) The coating composition according to (15) or (16), wherein the chitin nanofibers are those according to any one of (6) to (8).
(18) A method for producing a coating composition, comprising blending an aqueous suspension of chitin nanofibers with a water-soluble resin or emulsion.
(19) The method according to (18), wherein the chitin nanofiber is any one of (6) to (8).
(20) A material derived from a chitin-containing organism,
Subject to at least one deproteinization step and at least one decalcification step and at least one deacetylation step;
A method for producing chitosan nanofibers, which is subjected to a defibrating process.
(21) The method according to (20), wherein each step is always performed without drying.
(22) A chitosan nanofiber obtained by the method according to (20) or (21).
(23) The chitosan nanofiber according to (22), wherein the width of the fiber is 2 nm to 40 nm.
(24) A coating composition comprising chitosan nanofibers and a water-soluble resin or emulsion.
(25) The coating composition according to (24), wherein the chitosan nanofiber is as described in (23).
(26) A method for producing a coating composition, comprising blending an aqueous suspension of chitosan nanofibers with a water-soluble resin or emulsion.
(27) The method according to (26), wherein the chitosan nanofiber is as described in (23).

In one aspect, the present invention provides:
A bio-derived material derived from chitin
Subject to at least one deproteinization step and at least one decalcification step;
Provided is a method for producing chitin nanofibers, which is subjected to a defibrating process.

  The chitin nanofiber of the present invention can be obtained from a material derived from a chitin-containing organism. Examples of chitin-containing organisms include, but are not limited to, crustaceans, insects, and krill. Examples of the material derived from a chitin-containing organism as a raw material for the chitin nanofibers of the present invention include insect shells, krill shells, crustacean shells, shells, and the like. As materials derived from chitin-containing organisms, organisms with a high chitin content, for example, shells and hulls of crustaceans such as shrimps and crabs are preferred. Shrimp, crab shells, shells, etc. occupy most of the parts discarded after consumption. In addition, since shrimp and crabs are consumed in large quantities, shrimp and crab skins can be obtained in large quantities, which is convenient.

  Since chitin nanofibers in a living body have a matrix containing protein and calcium carbonate existing around and in the gap, they cannot be obtained unless dematrixing is performed. According to the method for producing chitin nanofibers of the present invention, it is possible to isolate and extract chitin nanofibers in a living body as they are. Therefore, the chitin nanofibers obtained by the production method of the present invention are thin and homogeneous, long, molecules are extended chain crystals, and have high strength. An extended chain crystal is a fibrous crystal that is regularly arranged in a state in which a rigid polymer is fully stretched to form a bundle, and since it has few defects, it can exhibit strong physical properties. . In particular, since chitin of crustaceans such as shrimps and crabs are highly crystalline alpha chitin, chitin nanofibers obtained from crustacean shells such as shrimps and crabs in the present invention have the above-mentioned excellent characteristics. Is remarkable.

  Deproteinization removes the protein that forms the matrix surrounding the chitin nanofibers. Examples of the deproteinization treatment include an alkali treatment method and a proteolytic enzyme method such as protease, and the alkali treatment method is preferred. In deproteinization by alkali treatment, an aqueous solution of an alkali such as potassium hydroxide, sodium hydroxide, or lithium hydroxide is preferably used, and the concentration depends on the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc. Depending on the case, it is usually selected from about 2 to about 10% (w / v), preferably about 3 to about 7% (w / v), for example about 5% (w / v). The temperature of deproteinization by the alkali treatment can be appropriately selected according to the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc., but is usually about 80 ° C. or higher, preferably about 90 ° C. or higher, Preferably, it is carried out while refluxing an alkaline aqueous solution. The treatment time can also be appropriately selected depending on the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc., but it is usually several hours to about 3 days, preferably several hours to about 2 days. Good.

  The deashing removes the ash that surrounds the chitin nanofibers, mainly calcium carbonate. The decalcification treatment includes an acid treatment method and an ethylenediamine tetraacetic acid treatment method, and an acid treatment method is preferred. In deashing by acid treatment, an aqueous solution of hydrochloric acid is preferably used, and the concentration thereof can be appropriately selected according to the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc. It is 4 to about 12% (w / v), preferably about 5 to about 10% (w / v). The temperature of deproteinization by acid treatment can be appropriately selected according to the amount of chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc., but is usually about 10 to about 50 ° C., preferably about 20 to about It may be 30 ° C., for example room temperature. The decalcification time by the acid treatment can be appropriately selected according to the amount of the material derived from the chitin-containing organism, the kind of the chitin-containing organism, the site, etc., but usually several hours to several days, preferably about 1 to about 3 days. For example, you may carry out for 2 days.

  Next, the outer skin (mostly chitin nanofibers) obtained in the above process is defibrated to obtain the target chitin nanofiber. Since chitin nanofibers are hydrogen-bonded and strongly aggregated when dried, it is preferable to perform each step of the method for producing chitin nanofibers of the present invention without always drying the material. For the defibrating treatment, an apparatus such as a stone mill grinder, a high-pressure homogenizer, and a freeze grinding apparatus can be used, and the grinder treatment is preferably performed using a stone mill grinder. If a device capable of applying a stronger load, such as a stone mill, is used, it is possible to quickly disentangle even shell-derived alpha chitin such as crabs and shrimps. Thereafter, the obtained chitin nanofibers may be dispersed in an aqueous medium such as water.

  In the above method for producing chitin nanofibers, a decoloring step may be performed if necessary or desired. The decolorization step may be performed at any stage of the above method, but is preferably performed after the deproteinization and decalcification treatments are completed. Decolorization may be carried out by any method, but it is preferable to use a chlorine bleaching agent, an oxygen bleaching agent, or a reducing bleaching agent. For example, about 1 to about 2% of hypochlorous acid in a buffer solution such as an acetate buffer solution. It may be carried out with sodium chlorate at about 70 to about 90 ° C. for several hours.

  Furthermore, a pulverization step may be performed in order to efficiently perform the deproteinization step, the deashing step, the decolorization step, the defibration step, and the treatment with the acidic reagent described below. The pulverization step may be performed at any stage of the above method, but is preferably performed immediately before the defibration step. The pulverization step may be performed by any method, but a method such as a homogenizer treatment or a mixer treatment is preferable, and may be performed by, for example, a household food processor.

  The steps such as the deproteinization step, the deashing step, the decolorization step, and the pulverization step may be repeated, repeated a plurality of times, or alternately. Moreover, the order of each process is not ask | required.

  Furthermore, if necessary or desired, the water-dispersibility of chitin nanofibers may be improved by treating the decalcified chitin-containing material with an acidic reagent. The treatment method with an acidic reagent is not particularly limited as long as it is a method for allowing the acidic reagent to penetrate into the material. The treatment with an acidic reagent can be typically performed by immersing the decalcified chitin-containing material in an aqueous acid solution. In this step, not only the improvement in water dispersibility but also the variation in the width (or diameter) of the chitin nanofibers can be suppressed. The acid that can be used in this step may be any acid and is not particularly limited, but a weak acid is preferred. Examples of the weak acid include, but are not limited to, acetic acid, formic acid, chloroacetic acid, fluoroacetic acid, propionic acid, butyric acid, lactic acid, citric acid, malonic acid, and ascorbic acid. The preferred weak acid used in this step is acetic acid. In this step, the pH of the aqueous weak acid solution is usually adjusted to about 2 to about 5, preferably about 2.5 to about 4.5, such as about 3 to about 4. The temperature of this step can be appropriately selected according to the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc., but is usually about 10 to about 50 ° C., preferably about 20 to about 30 ° C., For example, it may be room temperature. The treatment time of this step can also be appropriately selected according to the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc., but is usually 1 hour to about 1 day, preferably about 3 to about 12 hours. For example, it may be overnight. This acid treatment step may be performed at any stage before the defibration step, but preferably after the deproteinization and decalcification, the purification of chitin nanofibers proceeds to some extent. It may be performed immediately before the defibrating step.

  In another aspect, the present invention provides chitin nanofibers obtained by the above production method. As described above, according to the production method of the present invention, chitin nanofibers in a living body can be isolated and extracted as they are, and the chitin nanofibers obtained by the production method of the present invention are thin. It is homogeneous and very long, and the fibers are elongated and have chain fine crystals and high strength. Therefore, the chitin nanofibers obtained by the production method of the present invention are excellent in any of physical properties, ease of processing operation, and accumulated amount. Therefore, it can be applied to many uses. The width (or diameter) of the chitin nanofibers obtained by the present invention is usually about 2 nm to about 30 nm, preferably about 2 nm to about 20 nm, for example, 5 nm to 20 nm. Here, for example, “the width (or diameter) of the chitin nanofiber is about 2 nm to about 20 nm” is a fiber whose width (or diameter) is about 2 nm to about 20 nm or less when observed with an electron microscope. Occupies about 50% or more of the whole, preferably about 60% or more, more preferably about 70% or more. Further, the same applies to the width (or diameter) of chitosan nanofibers described later.

  Since chitin nanofibers have high crystallinity, they have excellent physical properties not found in other nanofibers. As mentioned above, crustaceans, especially shrimp and crab shells and shells, are discarded in large quantities. Obtaining useful chitin nanofibers from these is an environmentally friendly technology and also advantageous in terms of cost. is there. Furthermore, as described above, the chitin nanofibers obtained by the present invention have excellent physical properties. Therefore, this invention applies the outstanding physical property of the chitin nanofiber obtained by this invention to resin and a coating material.

  Accordingly, the present invention, in yet another aspect, provides a composite material including chitin nanofibers and a resin, and a method for producing the same. The chitin nanofibers used in the composite material of the present invention and the production method thereof are not particularly limited, but chitin nanofibers obtained by the method of the present invention described above are preferable. The chitin nanofiber produced by the method of the present invention is strong in strength because the fiber state is an extended chain crystal, has flexibility, and the width (or diameter) of the chitin nanofiber is relatively narrow. Is from about 2 nm to about 30 nm, preferably from about 2 nm to about 20 nm. Therefore, when the chitin nanofiber obtained by the method of the present invention is used, the composite material is further reinforced, the flexibility is increased, and the light transmission (transparency) is also improved. These features are particularly advantageous when the composite material is plastic. The composite material generally refers to a material in which two or more kinds of base materials are combined and integrated. The composite material in the present invention may be any kind of composite material in which chitin nanofibers are combined with other base materials, such as plastics or resins containing chitin nanofibers, chitin nanofibers and living bodies. Examples include combinations with materials, blending chitin nanofibers into paper, and combinations of chitin nanofibers with natural or synthetic fibers.

  The composite material containing the chitin nanofibers of the present invention can be produced by mixing chitin nanofibers with other materials and integrating them. The other material can be appropriately selected according to the use of the composite material and the necessary physical properties, and may be either a natural material or an artificial material. The method of mixing and integrating chitin nanofibers with other materials may also be a method known in the art and can be selected as appropriate. Below, the case where a plastic is manufactured as an example of the composite material of this invention is demonstrated. The plastic containing chitin nanofibers of the present invention can be produced by polymerizing a resin monomer in the presence of chitin nanofibers. The type of the resin monomer and the type of the polymerization initiator can be appropriately selected by those skilled in the art. Resin monomers that can be used in the production of the plastic of the present invention include monoacrylate monomers, diacrylate monomers, triacrylate monomers, monomethacrylate monomers, dimethacrylate monomers, trimethacrylate monomers, epoxy resin monomers, phenols Examples include, but are not limited to, resin monomers, melamine resin monomers, polyester monomers, polyimide monomers, and the like. Examples of the polymerization initiator that can be used for the production of the composite material of the present invention include 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-phenylpropan-1-one, azobisisobutyronitrile, and benzoyl peroxide. However, it is not limited to these. The ratios of chitin nanofiber, resin monomer, and polymerization initiator can be appropriately selected depending on properties such as the strength, flexibility, and transparency of the plastic to be obtained. A specific procedure for producing the chitin nanofiber-containing plastic of the present invention is illustrated. First, an aqueous suspension of chitin nanofibers is dehydrated by a known method such as filtration, compression, and drying to form a desired shape (for example, a sheet shape, a film shape, etc.). Means and methods for filtration, compression and drying used in this step are also known. Next, the chitin nanofibers molded into a desired shape are immersed in a resin monomer containing a polymerization initiator. In this step, a resin monomer containing a polymerization initiator is injected into chitin nanofibers. In this injection step, the injection of the resin monomer may be promoted by reducing the pressure. Then, a plastic can be obtained by reacting the polymerization initiator in the chitin nanofibers into which the resin monomer has been injected. The polymerization reaction conditions can be appropriately selected according to the type of resin monomer, polymerization initiator, desired plastic shape and size. In the above description, the plastic shape of the present invention is exemplified by a sheet shape, a film shape, etc., but using a known means / method, a powder shape, a fiber shape, a rod shape, a block shape, a sponge shape, a pellet shape, etc. It can also be formed into other shapes. Furthermore, additives (for example, flame retardants, plasticizers, filling / reinforcing materials, light weight imparting materials, nucleating agents, curing agents, impact resistance imparting agents, couplings for modifying and imparting functions of the plastic of the present invention. Agents, foaming agents, colorants, antioxidants, light stabilizers, UV absorbers, antistatic agents, conductivity-imparting agents, antibacterial and antifungal agents, antifogging agents, lubricants, heavy metal deactivators, etc.) and coloring An agent may be included as appropriate.

As described above, the chitin nanofiber-containing composite material of the present invention is reinforced more than a material containing no chitin nanofibers. The chitin nanofiber-containing composite material obtained by the present invention may have reduced thermal expansibility. Depending on the amount of chitin nanofibers contained, the coefficient of thermal expansion is, for example, 50 × 10 ⁻⁵ / ° C. or less, preferably about 30 × 10 ⁻⁵ / ° C. or less, more preferably about 10 × 10 ⁻⁵ / ° C. In the following, it is possible to obtain a product that is more preferably reduced to about 2 × 10 ⁻⁵ / ° C. or less. In addition, the thermal expansibility of the chitin nanofiber containing composite material obtained by this invention can be measured using a well-known means, for example, a thermomechanical measurement apparatus (TMA). Moreover, the composite material containing chitin nanofibers obtained by the present invention reflects not only the strength but also the flexibility, reflecting the properties of chitin nanofibers.

  The chitin nanofiber-containing composite material obtained by the present invention is less deteriorated in light transmission (transparency) than the case of not containing chitin nanofibers. In particular, by producing a composite material using a resin having the same or similar refractive index as that of chitin, a material with little decrease in light transmittance (transparency) can be obtained. Examples of resins having the same or similar refractive index as chitin include, but are not limited to, tricyclodecane methanol dimethacrylate, ethoxylated bisphenol A dimethacrylate, ethoxylated bisphenol A dimethacrylate, and the like. The chitin nanofiber-containing composite material obtained by the present invention has a linear transmittance in visible light of, for example, about 70% or more, preferably about 75% or more, depending on the type of resin and the amount of chitin nanofibers contained. More preferably about 80% or more, still more preferably 85% or more can be obtained. In addition, the linear transmittance | permeability in visible light of the chitin nanofiber containing composite material obtained by this invention can be measured, for example using an ultraviolet visible spectrophotometer. Furthermore, the chitin nanofiber-containing composite material obtained by the present invention is different from the chitin nanofiber-free composite material of the same thickness, although it depends on the type of resin, the amount of chitin nanofibers contained, and the thickness of the composite material. The loss of visible light transmittance, for example, the loss of transmittance at 600 nm, is about 10% or less, preferably about 5% or less, and more preferably about 2% or less. In addition, the transmittance | permeability of the light in the specific wavelength of the chitin nanofiber containing composite material obtained by this invention can also be measured, for example using an ultraviolet visible spectrophotometer.

  Therefore, the composite material of the present invention is suitable for applications that require strength and transparency, and in particular, can be used in place of conventionally used plastics. Typical usage examples include various daily necessities; outer parts and parts of electronic devices such as mobile phones, personal computers and lighting equipment; bodies of vehicles such as automobiles, ships and airplanes; sports such as rackets, golf clubs and fishing rods. Examples include, but are not limited to, supplies.

  The present invention also provides a coating composition comprising chitin nanofibers and a water-soluble resin or emulsion, and a method for producing the same. Chitin is insoluble in various solvents, but chitin nanofibers are highly dispersible in the solvent and can be used in coating compositions. Preferred chitin nanofibers used in the coating composition of the present invention and the production method thereof are chitin nanofibers produced by the production method of the present invention. The chitin nanofibers produced by the production method of the present invention are homogeneous, and the width (or diameter) is usually about 2 nm to about 30 nm (preferably about 2 nm to about 20 nm), so that the nanosize effect is large and Since the dispersibility is extremely high, it is suitable for use in a coating composition.

  Chitin nanofibers have cationic charge properties, are excellent in metal adsorptivity, pigment adsorptivity, antibacterial properties, solvent resistance, film-forming properties, and are highly reactive. Therefore, the coating composition containing chitin nanofibers obtained by the production method of the present invention and a water-soluble resin or emulsion is considered to have a new functionality that has not existed before. Furthermore, the coating composition containing chitin nanofibers obtained by the production method of the present invention and a water-soluble resin or emulsion forms a uniform coating film and has excellent adhesion to various objects to be coated.

  Furthermore, a water-soluble resin or emulsion having compatibility with a cationic polymer such as chitosan is extremely rare and very disadvantageous as a coating composition. On the other hand, chitin nanofibers are almost neutral polymers and can be mixed with a wide range of resins. Already commercialized chitosan-containing paints are acidic paints (chitosan can only be dissolved in an acidic solution), so that coating on metal surfaces is generally unsuitable. Also, the painting of wood parts such as building materials and furniture has been avoided when metal such as nails are combined. On the other hand, by using chitin nanofibers, it was possible to make a paint under neutral conditions, and it became easy to paint on metal. Therefore, the coating composition of the present invention can be used for metal.

  Already commercialized chitosan paint has extremely high hygroscopicity, and water droplets are formed on the surface of the paint film in a high humidity atmosphere (brushing phenomenon). It was necessary to paint. On the other hand, since it has a lower polarity than chitin nanofiber chitosan and is highly crystalline, the hygroscopicity is not as high as that of chitosan, so the coating composition of the present invention does not require such air conditioning equipment.

  Examples of a general method for producing a coating composition containing the chitin nanofibers of the present invention and a water-soluble resin or emulsion include an aqueous suspension of chitin nanofibers obtained by the production method of the present invention, a water-soluble resin or A method including a step of blending the emulsion may be mentioned. The blending can be performed by a known method such as mixing, mixing, stirring, sonication, dispersion, supercritical processing, or the like. The water-soluble resin and emulsion to be blended are any water-soluble synthetic resin, natural water-soluble resin, synthetic resin emulsion, or natural resin emulsion that can be mixed with or compatible with the chitin nanofiber aqueous suspension. May be. Examples of water-soluble synthetic resins that can be used in the production of the coating composition of the present invention include polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polyethyleneimine, polyallylamine, and polyaminesulfone. , Polyacrylic acid, sodium polyacrylate, acrylic acid / maleic acid copolymer salt, acrylic acid / sulfonic acid monomer copolymer salt, and the like, but are not limited thereto. Examples of natural water-soluble resins that can be used in the production of the coating composition of the present invention include chitosan, carboxymethyl chitosan, hydroxymethyl chitosan, hydroxyethyl chitosan, hydroxypropyl chitosan, and other chitosan derivatives, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, Cellulose derivatives such as methylcellulose, dextran, pullulan, sodium alginate and potassium alginate, alginate such as calcium alginate, ammonium alginate, chondroitin sulfate, tannic acid, carrageenan, pectin, gum arabic, guar gum, locust bean gum, tamarind gum, xanthan gum, Examples include curdlan, collagen, fucoidan, polyglutamic acid, polylysine, etc. It is, but is not limited thereto. Synthetic resin emulsions that can be used in the production of the coating composition of the present invention include vinyl acetate homopolymer, vinyl acetate / acrylic copolymer, ethylene / vinyl acetate copolymer, acrylic, acrylic / styrene emulsions, and the like. The urethane, silicone, fluorine monomer, prepolymer copolymer, and the like are not limited thereto. Examples of the natural resin emulsion that can be used in the production of the coating composition of the present invention include gum rosin, wood rosin, tall oil rosin, terpene resin, shellac resin, casein, copal rubber, carnauba wax, and taracant gum. For example, but not limited to. Conditions of the water-soluble resin or emulsion, blending ratio of chitin nanofibers and water-soluble resin or emulsion, blending temperature, time, etc. can be appropriately selected by those skilled in the art.

  Furthermore, in the above production method, by selecting a blending resin or emulsion having the same or similar refractive index as that of chitin, a highly transparent film that is transparent and excellent in light guiding properties after the coating film is formed is obtained. Can do. Examples of blending resins having the same or similar refractive index as chitin include polystyrene, acrylic / styrene copolymers, and also urethanes, silicones, fluorine monomers or prepolymer copolymers. It is not limited to these. Examples of emulsions having the same or similar refractive index as chitin include styrene-based, acrylic / styrene-based emulsions, and urethanes, silicones, fluorine monomers or prepolymer copolymers. However, it is not limited to these. In addition, by selecting organic resin beads for blending or inorganic powder having the same or similar refractive index as chitin, it is transparent after coating film formation and has excellent strength, light guide and scattering properties. A high film can be obtained. Examples of resin beads for blending that have the same or similar refractive index as chitin include acrylic resins, styrene resins, acrylic / styrene copolymers, and urethanes, silicones, fluorine monomers or prepolymer copolymers, etc. However, it is not limited to these. Examples of the inorganic powder having the same or similar refractive index as chitin include, but are not limited to, crushed glass, quartz, and mica.

  A pigment may be added for the purpose of coloring the resin composition of the present invention. Examples of pigments to be added include inorganic inorganic pigments, synthetic inorganic pigments, inorganic pigments represented by ceramic pigments, such as zinc white, lead white, lithopone, titanium dioxide, precipitated barium sulfate and barite powder, red lead, oxidation Iron red, yellow lead / chrome yellow [1], zinc yellow (1 type of zinc yellow, 2 types of zinc yellow), ultramarine blue, prussian blue (potassium ferrocyanide), carbon black, carbon black zircon gray, praseodymium yellow , Chrome titanium yellow, chrome green, peacock, Victoria green, bitumen, vanadium zirconium blue, chrome tin pink, pottery red, salmon pink, and the like, but are not limited thereto. Alternatively, organic pigments represented by azo pigments and polycyclic pigments such as anthraquinone, quinacridone, diketo-pyrrolo-pyrrole, perylene, indigoid, perinone, perylene, pyrazolone, pyranthrone, imidazolone, diketo-pyrrolo-pyrrole, Add quinophthalone, isoindolinone, pyrazolone, imidazolone, flavatron, phthalocyanine, perylene, nitroso, carbonium, phthalocyanine, anthraquinone, indigoid, carbonium, quinacridone, dioxazine, anthraquinone, perylene, imidazolone, indigoid, xanthene, carbonium, violanthrone, etc. However, it is not limited to these.

  In an increasing sense, so-called extender pigments such as calcium carbonate, talc and perlite may be added to the coating composition of the present invention. Furthermore, additives such as a dispersant, a thickener, an antifoaming agent, a leveling agent, and an anti-settling agent may be appropriately added to the coating composition of the present invention.

  In another aspect of the present invention, the chitin-containing material is subjected to at least one deproteinization step, at least one decalcification step, and at least one deacetylation step, and then a defibration step. A method for producing chitosan nanofibers is provided. The deproteinization step, the deashing step, and the defibration step are the same as described above with respect to the production of chitin nanofibers. In the present invention, the deproteinization step and the deacetylation step can be performed simultaneously. Furthermore, it is also possible to produce chitosan nanofibers by subjecting a commercially available chitin powder that has already undergone a deproteinization step and a deashing step to a deacetylation step. Although several methods are known as the deacetylation method, an alkali treatment method is preferable. In the deacetylation by alkali treatment, an aqueous solution of an alkali such as potassium hydroxide, sodium hydroxide or lithium hydroxide is preferably used, and its concentration is usually about 20 to about 50% (w / v), preferably about 30 to about 40% (w / v), for example about 40% (w / v). The temperature of deacetylation by alkali treatment can be appropriately selected according to the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc., but is usually about 80 ° C. or higher, preferably about 90 ° C. or higher, More preferably, it is carried out while refluxing an alkaline aqueous solution. The treatment time can also be appropriately selected according to the amount of the chitin-containing organism-derived material, the type of chitin-containing organism, the site, etc., but it is usually 30 minutes to about 3 days, preferably 30 minutes to overnight. . In addition, since chitosan nanofibers are hydrogen-bonded and strongly agglomerate when dried, it is very preferable to perform each step of the method for producing chitosan nanofibers of the present invention without always drying the material.

  In a further aspect, the present invention provides a composite material such as a plastic comprising chitosan nanofibers and a resin, and a coating composition such as a paint comprising chitosan nanofibers and a water soluble resin or emulsion. Chitosan nanofibers used for such composite materials and coating compositions may be any and are not particularly limited. However, the chitosan nanofibers produced by the method of the present invention are strong in strength because the fiber state is an extended chain crystal, have flexibility, and have a relatively narrow width (or diameter). Therefore, it can be preferably used for the composite material and the coating composition of the present invention. The width (or diameter) of chitosan nanofibers produced by the production method of the present invention is usually about 2 nm to about 40 nm. The composite material containing chitosan nanofibers obtained by the above-described production method of the present invention has increased strength as compared with those not containing chitosan nanofibers, and a highly transparent material can be obtained. Examples of the composite material containing the chitosan nanofiber of the present invention include plastic. The use of the composite material comprising chitosan nanofibers of the present invention is similar to that described above for the composite material comprising chitin nanofibers. Moreover, the coating composition containing the chitosan nanofiber obtained by the said manufacturing method of this invention forms a uniform coating film, and has the outstanding adhesiveness with respect to various to-be-coated objects.

  In a further aspect, the present invention provides a method for producing a composite material comprising chitosan nanofibers and a resin, and a method for producing a coating composition comprising chitosan nanofibers and a water-soluble resin or emulsion. These manufacturing methods include the above-described method for manufacturing a composite material including chitin nanofibers and a resin, and a paint composition including chitin nanofibers and a water-soluble resin or emulsion, except that chitosan nanofibers are used instead of chitin nanofibers. It is the same as the manufacturing method of a thing.

  EXAMPLES Hereinafter, the present invention will be described in more detail and specifically with reference to examples, but the examples should not be construed as limiting the present invention. Unless otherwise specified,% in the examples is weight / volume%.

Production of chitin nanofibers from crab shell (1)
Dried crab shell (from Canada, purchased from Kawai Fertilizer, 100 g) was added to 5% KOH aqueous solution and refluxed for 6 hours to remove protein in the crab shell. The treated crab shell was filtered and washed well with water until neutral. The crab shell was stirred with 7% aqueous HCl at room temperature for 2 days to remove ash in the crab shell. The crab shell was filtered again and washed well with water until neutral. The treated crab shell was added to a 0.3 M sodium acetate buffer solution of 1.7% NaClO ₂ and stirred at 80 ° C. for 6 hours to remove the pigment contained in the crab shell. The crab shell was filtered again and washed well with water until neutral. Crab shells were dispersed in water and the dispersion was crushed with a home mixer, and then acetic acid was added to adjust the pH to 3-4, followed by stirring overnight. The acetic acid-treated crab shell was subjected to a stone mill type grinder (Supermass colloider (MKCA 6-2)) to defibrate chitin nanofibers. The yield of chitin nanofibers was 12%. Moreover, the substitution degree of the N-acetyl group of the chitin nanofiber obtained by elemental analysis was 95%.

  The obtained chitin nanofibers were observed with a scanning electron microscope (FE-SEM) (JSM-6700F, JEOL). Most of the fibers had a width of about 20 nm or less, and many very thin and long homogeneous nanofibers having a width of about 10 nm were observed (FIG. 1). When nanofibers obtained using an infrared spectrophotometer (FT-IR) were evaluated, it was confirmed that they were purified chitin free from proteins and calcium carbonate (FIG. 2). Evaluation of chitin nanofibers obtained using an X-ray scattering measurement apparatus (XRD6000, Shimadzu) confirmed that it was α-type crystalline nanofibers (FIG. 3).

Production of chitin nanofibers from crab shell (2)
Dried crab shell (from Canada, purchased from Kawai Fertilizer, 100 g) was added to 5% KOH aqueous solution and refluxed for 6 hours to remove protein in the crab shell. The treated crab shell was filtered and washed well with water until neutral. The crab shell was stirred with 7% aqueous HCl at room temperature for 2 days to remove ash in the crab shell. The crab shell was filtered again and washed well with water until neutral. The crab shell was added to 5% KOH aqueous solution and refluxed for 2 days to remove the protein in the crab shell. The treated crab shell was added to a 0.3 M sodium acetate buffer solution of 1.7% NaClO ₂ and stirred at 80 ° C. for 6 hours to remove the pigment contained in the crab shell. The crab shell was filtered again and washed well with water until neutral. Crab shells were dispersed in water and the dispersion was crushed with a home mixer, and then acetic acid was added to adjust the pH to 3-4, followed by stirring overnight. The acetic acid-treated crab shell was subjected to a stone mill type grinder (Supermass colloider (MKCA 6-2)) to defibrate chitin nanofibers. The obtained chitin nanofiber was used as a 1% chitin nanofiber aqueous dispersion. The yield of chitin nanofibers was 12.1%.

Production of chitin nanofibers from shrimp shell Fresh black tiger shell (10 g) was added to 5% KOH aqueous solution and refluxed for 6 hours to remove protein in shrimp shell. The treated shrimp shell was filtered and washed well with water until neutral. The shrimp shell was stirred with 7% aqueous HCl at room temperature for 2 days to remove ash in the shrimp shell. The shrimp shell was filtered again and washed well with water until neutrality. The treated crab shell was added to a 0.3M sodium acetate buffer solution of 1.7% NaClO ₂ and stirred at 80 ° C. for 6 hours to remove the pigment contained in the shrimp shell. The shrimp shell was filtered again and washed well with water until neutrality. The shrimp shell was dispersed in water and the dispersion was crushed with a home mixer, and then the shrimp shell was subjected to a stone mill (supermass colloider (MKCA 6-2)) to defibrate chitin nanofibers. The yield of chitin nanofibers was 16.7%. The obtained chitin nanofibers were observed with a scanning electron microscope (FE-SEM) (JSM-6700F, JEOL). Most of the fibers were about 20 nm or less in width, and many very thin and long homogeneous nanofibers having a width of about 10 nm were observed (FIG. 4).

Manufacture of a composite material containing chitin nanofibers A 0.7% chitin nanofiber (obtained in Example 1) aqueous suspension was filtered, and the obtained sheet-like molded product was sandwiched between fine metal mesh sheets. A weight was placed and dried at 80 ° C. overnight. Dimethacrylate resin monomer (NK ester DCP (manufactured by Shin-Nakamura Chemical Co., Ltd.)) in which the dried chitin nanofiber sheet was cut to 2 × 3 cm and 5% of a polymerization initiator (2-hydroxy-2-methylpropiophenone) was added ( The film was immersed in a refractive index n of 1.556) and injected under reduced pressure overnight at 5 mmHg or less. The chitin nanofiber sheet into which the resin monomer was injected was taken out, sandwiched between slide glasses, and the resin was cured using a UV irradiation apparatus (Spot Cure, manufactured by Ushio Electric). The irradiation energy was 20 J / cm ² . The obtained chitin nanofiber-containing film was carefully peeled from the slide glass.

The chitin nanofiber-containing film prepared by the above method had a thickness of 69 μm and a fiber content of about 63%. When the transparency of the chitin nanofiber-containing film obtained above was evaluated using an ultraviolet-visible spectrophotometer (UV-4100, Hitachi High-Tech. Corp.), the linear transmittance in visible light was 88. %, It was confirmed that the material was very transparent. For example, the transmittance loss due to chitin nanofibers was only 1.8% at a wavelength of 600 nm as compared to a transparent composite material containing no chitin nanofibers (FIG. 5). The thermal expansion property of the chitin nanofiber-containing film was evaluated using a thermomechanical measurement apparatus (TMA) (TM / SS6100, SII Nanotechnology Inc.). Measurement temperature range: 20 to 165 ° C., heating rate 5 ° C./min. As a result, the thermal expansion coefficient of the film containing no chitin nanofibers was 10.9 × 10 ⁻⁵ / ° C., whereas the thermal expansion coefficient of the chitin nanofiber-containing film was 1.6 × 10 ⁻⁵ / ° C. The thermal expansion could be reduced by 85% (FIG. 6). This is because chitin nanofibers have low thermal expansibility (thermal expansion coefficient: 0.7 × 10 ⁻⁵ / ° C.), so that the expansion of the film is suppressed by compositing. In addition, as shown in the photographs of FIGS. 5 and 6, the produced chitin nanofiber-containing film has flexibility, and bending, cracking, white turbidity, and the like were not observed when bending as shown in the photographs.

  Thus, the chitin nanofiber-containing film obtained by the present invention was highly transparent, high in strength, and flexible.

Manufacture of coating composition containing chitin nanofiber and water-soluble resin or emulsion 0.36 part of wetting agent Dynal 604 (manufactured by Air Products) is added to 71.09 parts of self-crosslinking acrylic emulsion JONCRYL 1980 (manufactured by BASF). , 10.80 parts of a 1% aqueous solution of chitin nanofiber (prepared separately), co-solvent Dowanol DPM (manufactured by Dow Chemical) 4.27 parts, Dowanol DPnB (manufactured by Dow Chemical) 3.06 parts, Dowanol PPH ( A mixed solution of 0.81 part (manufactured by Dow Chemical) was added and stirred for 1 hour. Next, 0.42 part of antifoaming agent Tego Foamex 805 (manufactured by Troy Chemical), 2.54 parts of polyethylene wax emulsion JONWAX 26 (manufactured by Johnson Polymer), 0.18 part of lubricant Tego Glide 440 (manufactured by Troy Chemical) are sequentially added. Added and stirred for an additional hour. Next, a mixed solution of 0.62 parts of Dowanol DPM prepared in advance and 0.63 parts of thickener Tafigel PUR 50 (manufactured by Ultra Additive) was added, and finally 5.23 parts of water was added and stirred for 1 hour. As a result, the desired coating solution was obtained.

  A uniform coating film was formed by applying the obtained coating liquid on a cedar board material (50 mm × 50 mm × 10 mm) by brush coating. Moreover, the coating film showed strong adhesiveness to the plate material, and as a result of conducting a cross-cut test (JIS 5600-5-5), no peeling was observed.

Production of chitosan nanofibers from shrimp shell Fresh black tiger shell (10 g) was added to 5% KOH aqueous solution and refluxed for 6 hours to remove protein in shrimp shell. The treated shrimp shell was filtered and washed well with water until neutral. The shrimp shell was stirred with 7% aqueous HCl at room temperature for 2 days to remove ash in the shrimp shell, and the crab shell was filtered again and washed well with water until neutrality. Add the treated crab shell to a 0.3 M sodium acetate buffer solution of 1.7% NaClO ₂ , stir at 80 ° C. for 6 hours to remove the pigment contained in the shrimp shell, and filter the shrimp shell again to neutralize it. Wash thoroughly with water until. After adding 40% sodium hydroxide to the shrimp shell from which protein, ash and pigments have been removed, nitrogen gas is constantly being blown in, the mixture is refluxed for 6 hours, deacetylated, and then filtered again to neutralize the shrimp shell. Wash thoroughly with water until. The shrimp shell was dispersed in water and the dispersion was crushed with a household mixer, and then the shrimp shell was subjected to a stone mill (supermass colloider (MKCA 6-2)) to defibrate chitosan nanofibers. The yield of chitosan nanofibers was 10%. The obtained chitosan nanofiber was observed with a scanning electron microscope (FE-SEM) (JSM-6700F, JEOL). Most of the fibers had a width of 40 nm or less, and many homogeneous nanofibers having an average of about 20 nm were observed (FIG. 7). Moreover, the substitution degree of the N-acetyl group of the chitosan nanofiber obtained from the result of elemental analysis was 33%.

Manufacture of coating composition containing chitosan nanofiber and emulsion Self-crosslinking acrylic emulsion JONCRYL 8383 (manufactured by BASF) 71.13 parts, wetting agent Dynal 604 (manufactured by Air Products) 0.36 parts was added and prepared in advance 1 hour after adding a mixed solution of 19.96 parts of 2% aqueous solution of chitosan nanofiber (separate production method), 1.55 parts of co-solvent Dowanol DPM (manufactured by Dow Chemical) and 3.59 parts of Dowanol DPnB (manufactured by Dow Chemical) Stir. Next, 0.42 part of antifoaming agent Tego Foamex 805 (manufactured by Troy Chemical), 2.58 parts of polyethylene wax emulsion JONWAX 26 (manufactured by Johnson Polymer), and 0.18 part of lubricant Tego Glide 440 (manufactured by Troy Chemical) are sequentially added. Added and stirred for an additional hour. Finally, 0.23 part of a thickener Cognos DSX-1550 (manufactured by Henkel) was added and stirred for 1 hour to obtain the desired coating solution.

  The present invention can be used in the field of using nanofibers. The present invention can also be used in the manufacture of composite materials and paints and in the fields where they are used.

Claims (21)

Chitin-containing materials derived from crustaceans ,
Subjected to at least one deproteinization step and at least one decalcification step;
Subject to a step of treating with an acidic reagent,
A method for producing chitin nanofibers, which is subjected to a defibrating process.   The method according to claim 1, wherein the acidic reagent is a weak acid and the pH in the treatment step is 3-4.   The method according to claim 1 or 2, wherein the defibrating step is carried out using one or both of a stone mill and a high-pressure homogenizer. Chitin-containing materials derived from crustaceans,
Subjected to at least one deproteinization step and at least one decalcification step;
Subject to a weak acid treatment step, then
A method for producing chitin nanofibers characterized by being subjected to a defibrating step, wherein the pH in the treatment step with weak acid is 3 to 4, and the defibrating step is performed using a stone mill or high-pressure homogenizer. The method according to any one of claims 1 to 3.   The method according to claim 1, wherein each step is always performed without drying.   The chitin nanofiber obtained by the method of any one of Claims 1-5.   The chitin nanofiber according to claim 6, wherein the fiber has a width of 2 nm to 20 nm.   The chitin nanofiber according to claim 6 or 7, wherein the fiber state is an extended chain crystal.   The composite material containing the chitin nanofiber of any one of Claims 6-8, and resin. The composite material according to claim 9, wherein the coefficient of thermal expansion is reduced to 2 × 10 ⁻⁵ ° C. ⁻¹ or less.   11. The composite material according to claim 9, wherein the transmittance loss at 600 nm is 10% or less as compared with a non-chitin nanofiber having the same thickness.   A method for producing a composite material, wherein a resin monomer is polymerized in the presence of the chitin nanofibers according to any one of claims 6 to 8.   The coating composition containing the chitin nanofiber of any one of Claims 6-8, and a water-soluble resin or emulsion.   A method for producing a coating composition, comprising blending an aqueous suspension of chitin nanofibers according to any one of claims 6 to 8 with a water-soluble resin or emulsion. Chitin-containing materials derived from crustaceans ,
Subject to at least one deproteinization step and at least one decalcification step and at least one deacetylation step;
A method for producing chitosan nanofibers, which is subjected to a defibrating process. The chitosan nanofiber obtained by the method of Claim 15 . The chitosan nanofiber according to claim 16 , wherein the fiber has a width of 2 nm to 40 nm. A coating composition comprising chitosan nanofibers according to claim 16 or 17 and a water-soluble resin or emulsion. The coating composition according to claim 18 , wherein the chitosan nanofibers are those according to claim 17 . A method for producing a coating composition, comprising blending an aqueous suspension of chitosan nanofibers according to claim 16 or 17 and a water-soluble resin or emulsion. 21. The method of claim 20 , wherein the chitosan nanofibers are those of claim 17 .

Images